I work for CohesiveFT, the guys who make the Elastic Server platform - so I am biased - but we use the platform to deliver projects to partners and customers. It allows us to set up assembly-time components for different projects and then build them into VMs on the fly for VMware, Parallels, Xen and EC2. The service has a tagging feature so you can tag software packages, server specifications and templates and keep your assets straight.
You can also create assembly portals (think a content management system for assembling virtual servers) which you can control or even let customers have access to customizing their own virtual servers.
http://www.elasticserver.com
